1. Field of the Invention
The present invention relates to subsea drilling riser assemblies.
2. Description of the Related Art
Marine drilling riser assemblies have seen use in drilling operations for some time. In subsea drilling it is useful to re-use piping and pipe connectors at the drill site when possible. This can be useful when, for example, the subsea assembly needs to be brought back onto the drilling rig for re-working and then returned into service. Over time drilling operations have seen drilling to greater water depths, causing drilling assemblies to experience increasingly greater pressures while undergoing increasingly greater tension forces associated with longer and deeper subsea installations. These factors and others continue to create the need for more advanced marine drilling riser assemblies that can withstand these increased forces.
Subsea drilling operations have traditionally been based on marine drilling riser assemblies having flange type connectors with heavy bolts or stab type connectors with locking dogs to connect pipe sections. Often a box and pin including either an external flange type connector or stab type connector are welded to the ends of a pipe section. Once mated, matching ends of a flange type connector system are then be bolted together to secure the connection joint. These types of connections can include both multi-riser and single-riser configurations. It would be desirable to have connection joints that can undergo greater subsea pressures, handle increased tension loads, have greater re-usability, and install relatively quickly. These characteristics would additionally allow for greater drilling depths and less man hours per installation.
Additionally, it would be desirable to have marine drilling riser assemblies that include some of the characteristics of the Merlin type pipe connectors. Merlin type pipe connectors are well known in the art for connecting pipes together and are disclosed in GB1573945, GB2033518, GB2099529, GB2113335 and GB2138089. For a Merlin type connector, the connection is formed by a tubular pin member having a frustoconical outer peripheral surface and a tubular box member having a generally frustoconical inner peripheral surface corresponding to the frustoconical outer peripheral surface of the pin member. In use, the two members, each associated with a pipe section are telescoped together and are axially locked together by mating annular projections and grooves provided on the said peripheral surfaces, the projections and grooves being spaced apart along the two surfaces.
In telescoping the two members together, they are initially telescoped until surface contact is made between crest surfaces of the projections and surfaces between the grooves at least at the ends of the overlapped portions of the surfaces. Hydraulic fluid under pressure is then typically supplied between the overlapped parts of the surfaces to expand the box member and/or contract the pin member to permit the members to be fully telescoped together or the members may simply be pushed together. Pressurized hydraulic fluid is also used to disengage the members by expanding the box member and/or contracting the pin member to bring the projections out of engagement with the corresponding grooves.